This invention relates in general to coking and in particular to a new and useful method of carbonizing cold-compacted briquettes and to an apparatus for carrying out the method.
Such methods are known in the art and also practiced on larger scales (see for example, "Eisen und Stahl (Iron and Steel)" No. 93, 1973, Page 24).
Pitch, tar, mineral oil residues, or even sulfite liquor from the cellulose industry, for example, are employed as the binder. The sulfite liquor is obtained during the wood pulping process where particularly calcium bisulfite is the reactant, and the liquor contains about 50% of solid matter. Which binder to use depends on the nature of coal to be briquetted and coked. For example, "enriching" binders will be admixed to lean coals, while "leaning" binders will be added to average and well caking coals. Enriching binders are pitch and tar, for example, and sulfite liquor is often employed as a leaning binder. Occasionally, however, it is advantageous to admix pitch and sulfite liquor at the same time.
In the prior art, such briquettes are carbonized in either a discontinuous or a continuous process. With a discontinuous carbonization, indirect heating may be provided and rich gas can be obtained. A difficulty arises, however, in that the individual briquettes adhere to each other and form large agglomerates instead of separate pieces, which entails considerable problems in the coke removal.
In a continuous carbonization, direct heating with hot gases is provided and the substances obtained from the briquettes during the coking process are partly combusted. The risk of agglomeration is reduced, but not excluded, and only a gas of relatively low calorific value is obtained. Another drawback is that the hot flue gases having a temperature of 1,000.degree. C. have a steam content of about 10% by volume, causing a gasification of a considerable proportion of the coke (2 to 4%), in the high-temperature portion of the coking shaft.
In a discontinuous coking process, the throughput, referred to a unit volume of the oven, approximately corresponds to that in a conventional chamber coking operation. The higher a throughput in a continuous coking process, however, as already mentioned, is redeemed by obtaining a gas of lower calorific value and by high losses in fixed carbon due to gasification reactions.
Further, in prior art discontinuous processes, only a compound degasification gas is obtained containing both the hydrocarbons of high calorific value produced at the low or medium coking temperature, and the total of the hydrogen liberated from the semicoke during the high-temperature carbonization. That is why no specific or differentiated use of the evolved gases is possible in the prior art methods. It is advisable to recycle these gases into the process again.